Internal combustion engines have incorporated pistons of two general types: single-piece pistons and pistons having multiple parts. Known multiple-part pistons have included a piston head and a separate piston skirt that are connected together by a connecting element to form the piston portion of a piston and connecting rod assembly. The different parts of the piston may be constructed of differing materials and, for example, the piston head may be fabricated from materials that withstand the high temperatures and pressures encountered in the combustion region of the cylinder and in the vicinity of the piston rings, while the piston skirt may be constructed of lighter weight materials so as to reduce engine weight. In both one-piece and multiple-part pistons, a connecting rod is connected to the piston through a bearing member, commonly provided as an integral element of the piston head, so that the connecting rod may pivot relative to the piston as the piston reciprocates within the cylinder.
An example of the known piston constructions is provided in U.S. Pat. No. 4,377,967, which discloses a two-piece piston assembly having an upper part or piston head made of cast iron, malleable iron or similar material and a lower part or piston skirt made of an aluminum-containing metal. The piston head and piston skirt are secured in desired relative positions and are movably connected to a connecting rod by a piston pin. More specifically, the piston head includes downwardly extending pedestals having bosses at their lower portions defining holes for receiving the piston pin. Similarly, the piston skirt includes holes that register with the pedestal bosses and also receive the piston pin coaxially with the holes of the piston head to thereby connect the piston head, piston skirt, and the connecting rod.
U.S. Pat. No. 5,701,802 discloses a multiple-part piston having separate piston head and piston skirt components and wherein each of the piston head and piston skirt integrally incorporate a bearing block having a bearing surface. A coupling device is provided for interconnecting the piston head and the piston skirt and for interconnecting the individual integral bearing blocks of those two components. The two bearing blocks are configured so that when interconnected they form a bearing for rotatably coupling a connecting rod to the piston.
U.S. Pat. No. 5,713,262 provides a piston including a piston head having a pair of pin bosses extending downward from the piston head. Two identically configured piston skirts extend from the piston bead and are arranged symmetrically about the bosses. Side walls are provided around the bosses and connect the bosses to the piston skirts. A piston pin is provided in the two bosses and pivotally couples a connecting rod to the piston.
Manufacturing the piston head to include elements of the bearing for coupling the connecting rod to the piston body complicates the manufacturing process and increases the associated costs. Moreover, integrating bearing elements for the connecting rod into the piston head allows for the ready conduction of heat to the bearing elements from regions of the piston head that encounter the temperatures of combustion and that experience frictional heat generated by moving contact between the piston rings and the cylinder. The heat conduction increases the temperature experienced at the piston/connecting rod interface (bearing) and may adversely affect the wear properties at the bearing. The integration of connecting rod bearing elements into the piston head also may complicate the assembly of the piston to the connecting rod and, as seen in existing piston designs, may require that the piston skirt have a complicated, non-uniform construction and, for example, include voids therethrough so that the piston pin may be inserted into the piston body to interconnect the connecting rod and the piston body.
Thus, based upon at least the foregoing deficiencies in existing piston and connecting rod assembly designs, the need exists for an improved design for a piston and connecting rod assembly that reduces the complexity and costs associated with manufacturing the assembly, reduces piston/connecting rod bearing temperatures so as to enhance bearing life, and reduces the weight of the final assembly.